A vacuum drying process is an important producing process during the electronic components manufacturing processing. The vacuum drying process can reduce water contained in the electronic components, such that the electronic components can meet the using requirement. The vacuum drying process is mainly applied to the manufacturing processes of the electronic components, especially applied to the manufacturing processes of the supercapacitor or the manufacturing processes of the lithium battery. The traditional vacuum drying device mainly includes a single vacuum drying oven, and electronic components needed to be dried are transported to the vacuum drying device through a material car, the traditional vacuum drying device is poor in processing efficiency, and cannot control the dry humidity and the temperature maintain highly uniform in a vacuum condition. A plurality of vacuum drying devices having accesses corresponding to each other can form a vacuum drying system which can continuously process, the vacuum drying devices can be set different vacuum degrees, drying temperatures, and drying times to overcome the above defects existed in the single vacuum drying device. However, when the materials are directly transported into the vacuum drying system, the materials cannot be dried efficiently, so an automatic vacuum preheating furnace can be matched and worked with the vacuum drying system to dry the materials efficiently. Now the automatic vacuum preheating furnace which can preheat the materials efficiently is in need.